Doppler renal resistivity index in horses: A systematic review.
Authors: Dos Santos Rosse Nathalia, Reis Emily Correna Carlo
Journal: Equine veterinary journal
Summary
# Doppler Renal Resistivity Index in Horses: Editorial Summary Renal resistivity index (RI)—a Doppler ultrasound measurement of arterial resistance within the kidney—offers potential for early detection of kidney disease in horses, since changes in blood perfusion may precede structural damage detectable by conventional imaging. Dos Santos Rosse and Reis conducted a systematic review of published literature on equine renal RI, searching four major databases through February 2023 and applying rigorous inclusion criteria to identify methodologically sound studies. Only five papers met inclusion criteria, all examining healthy, unsedated horses via transabdominal ultrasonography, revealing considerable heterogeneity in findings: the upper limit of normal for the right kidney RI was 0.58 ± 0.06 in untrained horses—substantially lower than the 0.70 reference value used in human medicine and small animal practice—though one study reported higher RI values in elderly horses compared with foals and adults, and two studies documented lateralised differences between kidneys. The paucity of available evidence and lack of standardised scanning protocols represent significant gaps in the literature, meaning practitioners cannot yet reliably incorporate renal RI assessment into routine clinical screening or follow-up of horses with renal compromise. Establishment of species-specific, age-related and lateralised reference ranges through prospective, methodologically consistent studies is essential before this potentially valuable diagnostic tool can be confidently applied in equine practice.
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Practical Takeaways
- •Current reference ranges for equine renal RI (0.58 ± 0.06) differ significantly from other species, so species-specific interpretation is essential when performing renal ultrasound
- •Standardised examination protocols are needed before renal RI can be reliably used as a clinical tool for early detection of kidney damage in practice
- •More research is needed before renal RI can be confidently incorporated into routine equine nephrology assessment
Key Findings
- •Only 5 eligible studies found from 134 identified, indicating scarce published data on equine renal resistivity index
- •Upper limit of normality for renal RI in untrained horses is 0.58 ± 0.06, substantially lower than the 0.70 value used for humans, cats and dogs
- •Heterogeneous outcomes across studies regarding laterality differences and age-related changes in renal RI
- •All included studies used transabdominal ultrasonography technique in healthy non-sedated horses